Process of treating derivatives of cellulose and product thereof



Patented Nov. 12, 1935 UNITED s-ra'rss PATENT OFFICE PROCESS OF TREATINGDERIVATIVES OF CELLULOSE AND PRODUCT THEREOF George W. Seymour,Cumberland, Md., assignor to Celanese Corporation of America, acorporation of Delaware No Drawing. Application April 12, 1932, SerialNo. 604,876

2 Claims.

This invention relates to a solvent for cellulose An object of myinvention is to produce a new solvent for cellulose acetate and otherderiva- 10 tives of cellulose. Another object of my invention is toemploy ethylene formal as a solvent for cellulose acetate or otherderivatives of cellulose in various processes and for the preparation ofvarious compositions. Other objects of 15 my invention will appear fromthe following detailed description.

As is well known, the number of substances that are solvents for eventhe acetone soluble type of celluloseacetate having an acetyl'value 20of 53 to 55% is very limited, and because of the small range of thesesolvents, it is often difii cult' or even impossibleto find a solventthat meets with the requirements of a given problem, such as boilingpoint, compatibility, or mutual solu- 25 bility with other solvents,resins or other ingredients present in the cellulose acetate compositionin which it is employed, cheapness, availability, etc.

. This problem of finding a suitable volatile sol- 3 vent for celluloseacetate of higher acetyl value,

say 56 to 62.5% is particularly difficult. Whereas cellulose triacetate,that is, cellulose. acetate having an acetyl value of 62.5% or othercellulose acetates of very high acetyl value have certain 35 propertiesthat for some purposes are superior to those of cellulose acetate oflower acetyl value and having optimumsolubility in acetone, heretoforeit has not been possible to form products therefrom commercially, sincethe very few 40 known solvents for such high acetyl value celluloseacetate are either chlorinated hydrocarbons which hydrolize to form freeacid that cor-t rodes the metallic apparatus in which they are employedand some of which are toxic, or else are objectionable for otherreasons. Moreover for most varieties of cellulose formate there are fewif any volatile, liquids known to have a true solvent action on thesame.

I have found that ethylene formal is an excel- 50 lent solvent for allvarieties of cellulose acetate from the acetone soluble type to thefully acetylated cellulose triacetate, as well as for other derivativesof cellulose, particularly organic de-' rivatives of cellulose and maybe employed in all 5 compositions and processes wherein celluloseacetate is to be dissolved. I have further found that ethylene formal isan excellent solvent for most varieties of cellulose formats.

The ethylene formal, also known as formal glycol or the methylene etherof ethylene glycol 5 having the structural formula may be prepared byheating under reflux equimolecular proportions of ethylene glycol andformaldehyde in the presence of HCl, sulfuric acid, or other suitablecatalysts. Its boiling point is 73 to 75 C. and it has a high solventpower for cellulose acetate and other organic derivatives of cellulose.Obviously the formal glycol or ethylene formal may be prepared in anyother suit-able manner.

The ethylene formal because of its boiling point of 73 to 75 C. may beused as a low boiling solvent in the preparation of solutions, plasticmasses or other products or for other purposes wherein it is desired todissolve partially or wholly derivatives of cellulose, particularly theorganic derivatives of cellulose such as organic esters of cellulose andcellulose ethers. Examples of organic esters of cellulose beingcellulose acetate, cellulose formate, cellulose butyrate, while examplesof cellulose ethers are ethyl cellulose, methyl cellulose and benzylcellulose. A few of the many instances of the use of ethylene formalwill be given.

The ethylene formal may be employed alone or in conjunction with otherlow boiling, medium, or high boiling solvents, resins both natural andsynthetic, plasticizers or other desired ingredients to prepare coatingcompositions or dopes containing cellulose acetate or other organicderivatives of cellulose, which coating compositions may be employed forcoating fabrics, wood and the like,,or as lacquers containing suitablenatural or synthetic resins, to be applied to metallic or other smoothsurfaces; Dopes containing the cellulose acetate dissolved in a solventcomprising ethylene formal may be cast on to smooth surfaces such asfilm bands, wheels and the like, to form upon evaporation of thesolvent, films which may be used for'photographic purposes, or thinfoils to be employed as transparent wrappings for packages offoodstuffs, tobacco products and other articles of commerce. Such dopesmay be extruded through orifices into an evaporative atmosphere, as indry spinning, or into a precipitating bath as in wet spinning, to formfilaments, yarns, bristles or straw.

Plastic compositions containing organic derivatives of cellulose,plasticizers and other desired ingredients may be made by the use ofethylene formal as at least part of the solvent during the kneading ofthe mass and subsequent working up of the same on heated malaxatingrolls.

If desired besides the ethylene formal other solvents or liquids may beused in addition thereto, such as low boiling solvents or other liquidslike acetone, ethylene dichloride and the like, and medium'and/or highboiling solvents such as ethyl acetate, ethyl lactate, tetrachlorethaneor diacetone alcohol. Examples of plasticizers for cellulose acetate arediphenylol propane, triacetin, dibutyl tartrate, diethyl phthalate,monomethylene xylene sulfonamid, triphenyl phosphate, etc.

Ethylene formal is an excellent solvent for the acetone solublecellulose acetate having an acetyl value of 52 to 55% and is indeed inmany respects superior to acetone itself as a solvent for such celluloseacetate, as is shown by the fact that solutions of the cellulose acetatein ethylene formal have higher clarity than corresponding solutions inacetone, and a greater quantity of diluent such as benzol or ethylalcohol may be added to the solution of the cellulose acetate in ethylformal before precipitation of the cellulose acetate takes place than inthe case of a corresponding solution in acetone.

An important application of my invention is the use of' ethylene formalas a volatile solvent inthe preparations of solutions, plastics, liquidcoating compositions, lacquers and the like containing cellulose acetateof high acetyl value, having an acetyl value of 56% up to and includingthe cellulose triacetate. As pointed out above there is no knowncommercially useful volatile solvent for cellulose tria'cetate or otherhighly" acetylated cellulose acetates. Indeed, even in the case ofcellulose acetates having an acetyl value of 56% to 58%, which areacetonesoluble, the production of filaments of fine denier is moredifficult than in the case when normal commercial cellulose acetateshaving an acetyl value of about 52% to 54% are employed. Not only isthis difiiculty found when acetone solutions of the cellulose acetateare employed, but itis also present in the case of the use of othersolvents or solvent mixtures, such as methylene chloride and mixtures ofmethylene or ethylene chloride and ethyl or' methyl alcohol. I havefound that by the use of ethylene formal as a solvent, it is possible toform solutions of cellulose acetate of acetyl value above 56% whichsolutions have high clarity and which may be spun by a dry spinningprocess to form fine filaments or denier as low as 2 up to 5, 6, 7 ormore,- a' result heretofore impossible of attainment.

1 Moreover, soluticns'of such high acetyl value cellulose acetate, saycellulose triacetate, in ethylene formal may be cast to form films. orfoils which are superior to films or .foils made from the ordinaryacetone soluble cellulose acet'ateiin many respects, such as greaterimpermeability'to moisture, greater resistance to cockling, crinklingand delustering when subjected to boiling water or boiling soapsolutions or other hot aqueous media, greater tensile strength, greaterresistance to the solvent action of various organic liquids and highermelting point. Yarns made of cellulose acetate of higher acetyl valuehave similar superior properties as compared to yarn made of theordinary acetone soluble cellulose acetate.

Plasticizers such as dibutyl tartrate, dimethyl phthalate, diethylphthalate and triacetin that are compatible with ordinary acetonesoluble cellulose acetate are compatible with the cellulose acetate ofhigher acetyl value and may be used in conjunction therewith for formingcoating compositions, plastics, films, filaments, etc.

In order further to illustrate my invention, but without being limitedthereto, the following specific examples are given.

Example I 1 part of cellulose acetate having an acetyl value of about58% is dissolved in 3 parts by weight'of ethylene formal. The solutionor dope thus formed is extruded through a spinning jet having holes of0.07 mm. in diameter into a cabinet through which air or otherevaporative atmosphere of a temperature of about C. is caused'to pass.The filaments so formed are drawn off and may be twisted together andwound on a cap spinning device to form yarn having the desirablecharacteristics above de- 3 scribed. In this manner filaments having adenier of 2 to '7 maybe formed.

' Example II Cellulose triacetate having an acetyl value of 62.5 isemployed for making films or foils. A solution is formed having thefollowing composition.

. Partsby weight Cellulose triacetate Plastici'zer 30 Ethylene 'formal500 The plasticizer may be dibutyl tartrate, dimethyl phthalate, diethylphthalate or triacetin or a mixture of two or more of these.

The solution so'formed is cast upon a smooth polished surface such asupon a film wheel and the solvent caused to evaporate, the film or foilso produced then being dried. Films or foils made in this manner havethe desirable properties above described.

In this specification the figures of acetyl value of thecellulose-acetate are calculated as-acetic acid. 7 4

It is to be understood that the foregoing delose acetate having anacetyl value above 58% dissolved in a volatile solvent consisting ofethylene-formal.

.- GEORGE W. SEYMOUR.

